A conventional process for providing a subject with eyewear such as glasses (a term which is used here to include both vision correction glasses (spectacles) and sunglasses, or even a headset for virtual reality (VR) or augmented reality (AR)) involves the subject trying on series of dummy frames, and examining his or her reflection in a mirror. Once a frame style has been selected, an optician conventionally makes a number of manual measurements of the subject's face, to obtain distance parameters of the subject's face, which are used to provide a bespoke frame including lenses. In the case of vision correction glasses, the lenses are chosen to have respective refractive power according to the visual deficiencies of the subject's respective eyes.
The measurement process is subject to various errors. For example, it is difficult to measure the distances of the eye to various portions of the lenses, which may be highly disadvantageous for glasses which perform visual correction. It has been estimated that a 2 mm variation of the spacing of the eye and the lens can result in a 10% difference in the resulting field of vision. Additional problems are that the modification of the frame changes the position of the optical centre of the lens in the up/down and left/right directions (relative to the face of the subject) which may also have undesirable optical effects.